1. Field of the Invention
The present invention relates to a capacitor for a semiconductor device and a fabricating method thereof, and more particularly, to a capacitor using a tantalum oxynitride (TaON) film as a high-permittivity dielectric film, and a fabricating method thereof.
2. Description of the Prior Art
As the overall dimensions of semiconductor devices continue to shrink, the demand is ever increasing for devices having large charge storage capacity. The need for large charge storage capacity remains even though individual components are scaled to smaller dimensions. As the surface area of a component, such as a capacitor, is reduced, a corresponding reduction in charge storage capability occurs. The smaller surface area available for components, such as transistors, capacitors, and the like, coupled with the requirement to maintain high charge storage levels, has led researchers in the field of fabrication science to seek new materials from which to construct the components. One group of promising new dielectric materials is the family of high-permittivity ferroelectric materials such as tantalum pentoxide (Ta2O5), BST ((Ba,Sr)TiO3), or PZT (Pb(Zr1xe2x88x92xTix)O3).
While the ferroelectric materials offer a substantial improvement in compact charge storage capability, the use of the ferroelectric components in MOS integrated circuit technology has been limited by the physical and chemical characteristics of the ferroelectric materials. For example, stoichiometrically the Ta2O5 film frequently runs short of oxygen, resulting in permittivity degradation and undesired leakage current characteristics. Moreover, the Ta2O5 film has a bad interface characteristic with a polysilicon film or a metal nitride film commonly used as an upper electrode, and is in a high intrinsic stress state, thus remaining many problems to be solved.
The high-permittivity dielectric capacitor using such a Ta2O5 film is generally fabricated by the following process.
First, a lower electrode is formed on an insulating layer overlying a semiconductor substrate. Next, a Ta2O5 film is formed on the lower electrode by thermally decomposing tantalum ethoxide Ta(OC2H5)5, a tantalum source gas, in an oxygen atmosphere. In order to remove oxygen vacancy which may exist in the Ta2O5 film, a post baking process is performed using ultraviolet (UV)xe2x80x94O3, or thermal treatment is performed in an oxygen atmosphere using O2, N2O, or O3 gas. Thereafter, an upper electrode is formed on the Ta2O5 film by chemical vapor deposition (CVD) or sputtering.
However, there are several drawbacks associated with the Ta2O5 film although Ta2O5 material has inherently higher dielectric properties.
First, when the Ta2O5 film is deposited, the stoichiometrical shortage of oxygen becomes severe by residual gases or byproducts, resulting in undesired leakage current increase.
Second, when post-thermal treatment is performed in an oxygen atmosphere and at a temperature of 800xc2x0 C. or more, gases are overflowed, and thus an amorphous Ta2O5 film is crystallized into a columnar structure. At this time, oxygen diffuses quickly along grain boundaries, and a silicon oxynitride (SiON) film is thus thickly formed between a polysilicon layer and a Ta2O5 film in the case of using a polysilicon layer as a lower electrode. This adversely effects the realization of high capacitance promised by the Ta2O5 film.
Third, in the case of using a titanium nitride (TiN) film as an upper electrode of a capacitor, an interface reaction occurs between the Ta2O5 film and the TiN film at a temperature of 500xc2x0 C., so that oxygen within the Ta2O5 film diffuses into the TiN film. Thus, the stoichiometrical shortage of oxygen is accelerated.
To solve the above problems, it is an object of the present invention to provide a high-permittivity dielectric capacitor with an enhanced film characteristics compared with conventional dielectric films.
It is another object of the present invention to provide a method of fabricating a capacitor for a semiconductor device that adopts a new dielectric material.
It is still another object of the present invention to provide a method of fabricating a capacitor for a semiconductor device by which interface heterogeniety between upper and lower electrodes is small, and current leakage due to oxygen vacancy is reduced.
Accordingly, to achieve the first object, there is provided a capacitor characterized in that a tantalum oxynitride (TaON) film is used as a high-permittivity dielectric material. Preferably, the tantalum oxynitride is formed to a thickness of 10 to 500 xc3x85.
To achieve the second and third objects, there is provided a method of fabricating a capacitor for use in a semiconductor device, characterized in that a tantalum oxynitride film is formed as a dielectric film on a lower electrode using chemical vapor deposition. In depositing the tantalum oxynitride film, tantalum ethoxide gas is used as a source of tantalum and oxygen, and ammonia gas is used as a source of nitrogen. The conditions of the CVD process are as follows.
Tantalum ethoxide gas is supplied at a flow rate of 0.01 sccm (standard cubic centimeters per minute) to 1 slm (standard liter per minute), and the ammonia gas is supplied at a flow rate of 10 sccm to 10 slm to the CVD reactor, respectively. The base pressure and the deposition pressure of the reactor are preferably set to be 1xc3x9710xe2x88x923 Torr or less, and between 1 mTorr and 100 Torr, respectively. The deposition temperature in the reactor is set to be between 150xc2x0 C. and 900xc2x0 C.
Hydrogen gas can be further supplied to activate decomposition of source gases in the step of chemical vapor depositing the tantalum oxynitride film.
Alternatively, plasma treatment can be further carried out with plasma power of 10 W to 3 kW to activate decomposition of the tantalum ethoxide gas.